by Kirsti Marohn, USA TODAY

The technology is designed to stop or slow a train automatically to prevent accidents, such as a collision with another train or a derailment from excessive speed.

The changes stem from federal legislation passed in 2008 after a commuter train collided head-on with a freight train in Chatsworth, Calif., killing 25 people and injuring 135. An investigation found the Metrolink train driver was sending and receiving text messages shortly before the crash.

Metrolink, a public entity that uses 388 miles of track in Southern California and owns 216 miles of it, expects to become the first commuter rail to use the technology.

Positive train control uses GPS technology to determine a train's location and speed. It warns train operators of potential problems, then overrides the driver and stops the train if the operator does not respond within a certain time.

The system requires equipment installed along rail lines as well as aboard locomotives. It's a complex endeavor expected to cost railroads more than $13 billion to install and maintain over the next 20 years, according to the Association of American Railroads, which represents major U.S. freight railroads and Amtrak.

Whether railroads will meet the 2015 deadline remains unclear. A report to Congress from the Federal Railroad Administration in August stated that because of "significant technical and programmatic issues" most railroads likely won't be able to put the technology totally in place by Dec. 31, 2015.

Despite best efforts and financial investments, it's becoming clear that meeting the deadline is no longer realistic, said Holly Arthur, a railroad association spokeswoman.

Each railroad's positive train control system is very complex and must operate with other railroads' systems, she said. The technology never has been used this way and must be designed, installed and tested before receiving federal certification.

"This has never been done before," Arthur said.

Work already has begun to upgrade signals along BNSF Railway lines in Minnesota and will continue this year, said Amy McBeth, a spokeswoman for the railroad that has 32,000 miles of track in 28 states and two Canadian provinces. BNSF has spent about $300 million on positive train control upgrades on its entire rail system this year.

"We are on track to meet that required deadline," she said. The traveling public probably won't notice any difference after the technology is installed.

Amtrak also will install positive train control aboard its trains that run along BNSF rail lines, spokesman Marc Magliari said.

Metro Transit, which operates the Northstar commuter rail line between Big Lake, Minn., and Minneapolis, expects to have its six locomotives and six cab cars outfitted with the equipment in 2014 after the wayside equipment is tested, spokesman John Siqveland said.

Metro Transit, which leases time on BNSF tracks to operate Northstar, has an agreement with the railway to pay for some of the costs. Northstar's share is expected to be about $2 million, Siqveland said.